All of lore.kernel.org
 help / color / mirror / Atom feed
From: Alexandru Elisei <alexandru.elisei@arm.com>
To: maz@kernel.org, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu
Subject: [PATCH 1/2] KVM: arm64: Return early from read_id_reg() if register is RAZ
Date: Mon, 27 Sep 2021 13:49:10 +0100	[thread overview]
Message-ID: <20210927124911.191729-2-alexandru.elisei@arm.com> (raw)
In-Reply-To: <20210927124911.191729-1-alexandru.elisei@arm.com>

If read_id_reg() is called for an ID register which is Read-As-Zero
(RAZ), it initializes the return value to zero, then goes through a list
of registers which require special handling.

By not returning as soon as it tests if the register is RAZ, it creates
the opportunity for bugs, if a patch changes a register to RAZ (like has
happened with PMSWINC_EL0 in commit 11663111cd49), but doesn't remove the
special handling from read_id_reg(); or if a register is RAZ in certain
situations, and readable in others.

Return early as to make it impossible for a RAZ register to be anything
other than zero.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 arch/arm64/kvm/sys_regs.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 1d46e185f31e..4adda8bf3168 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1064,7 +1064,12 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		struct sys_reg_desc const *r, bool raz)
 {
 	u32 id = reg_to_encoding(r);
-	u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
+	u64 val;
+
+	if (raz)
+		return 0;
+
+	val = read_sanitised_ftr_reg(id);
 
 	switch (id) {
 	case SYS_ID_AA64PFR0_EL1:
-- 
2.33.0

_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Alexandru Elisei <alexandru.elisei@arm.com>
To: maz@kernel.org, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu
Cc: james.morse@arm.com, suzuki.poulose@arm.com
Subject: [PATCH 1/2] KVM: arm64: Return early from read_id_reg() if register is RAZ
Date: Mon, 27 Sep 2021 13:49:10 +0100	[thread overview]
Message-ID: <20210927124911.191729-2-alexandru.elisei@arm.com> (raw)
In-Reply-To: <20210927124911.191729-1-alexandru.elisei@arm.com>

If read_id_reg() is called for an ID register which is Read-As-Zero
(RAZ), it initializes the return value to zero, then goes through a list
of registers which require special handling.

By not returning as soon as it tests if the register is RAZ, it creates
the opportunity for bugs, if a patch changes a register to RAZ (like has
happened with PMSWINC_EL0 in commit 11663111cd49), but doesn't remove the
special handling from read_id_reg(); or if a register is RAZ in certain
situations, and readable in others.

Return early as to make it impossible for a RAZ register to be anything
other than zero.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 arch/arm64/kvm/sys_regs.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 1d46e185f31e..4adda8bf3168 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1064,7 +1064,12 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		struct sys_reg_desc const *r, bool raz)
 {
 	u32 id = reg_to_encoding(r);
-	u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
+	u64 val;
+
+	if (raz)
+		return 0;
+
+	val = read_sanitised_ftr_reg(id);
 
 	switch (id) {
 	case SYS_ID_AA64PFR0_EL1:
-- 
2.33.0


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-09-27 12:48 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-27 12:49 [PATCH 0/2] KVM: arm64: Minor improvements to RAZ register handling Alexandru Elisei
2021-09-27 12:49 ` Alexandru Elisei
2021-09-27 12:49 ` Alexandru Elisei [this message]
2021-09-27 12:49   ` [PATCH 1/2] KVM: arm64: Return early from read_id_reg() if register is RAZ Alexandru Elisei
2021-09-30 13:22   ` Andrew Jones
2021-09-30 13:22     ` Andrew Jones
2021-09-27 12:49 ` [PATCH 2/2] KVM: arm64: Use get_raz_reg() for userspace reads of PMSWINC_EL0 Alexandru Elisei
2021-09-27 12:49   ` Alexandru Elisei
2021-09-30 13:29   ` Andrew Jones
2021-09-30 13:29     ` Andrew Jones
2021-10-06 14:49     ` Alexandru Elisei
2021-10-06 14:49       ` Alexandru Elisei
2021-10-06 15:23       ` Andrew Jones
2021-10-06 15:23         ` Andrew Jones
2021-10-06 15:35         ` Alexandru Elisei
2021-10-06 15:35           ` Alexandru Elisei
2021-10-11  9:47 ` [PATCH 0/2] KVM: arm64: Minor improvements to RAZ register handling Marc Zyngier
2021-10-11  9:47   ` Marc Zyngier

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210927124911.191729-2-alexandru.elisei@arm.com \
    --to=alexandru.elisei@arm.com \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=maz@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.